Do novel competitors shape species' response to climate change?

Background/Question/Methods

Climate change can have direct effects on species phenology, ecophysiology and demography, as well as indirect effects that are mediated by interactions with other species, such as competitors. While previous studies have investigated climate-mediated effects of competition among species that already co-occur within a community, some of the largest impacts are likely to arise as new species enter communities through migration. These effects have so far been neglected, at least partly because of uncertainty regarding the species composition of future communities, and the challenges of simulating such communities under realistic future climate scenarios. These problems are reduced along steep elevation gradients in mountains, because the species that will enter communities as climate warms will most likely be those that are already found only a few hundred meters lower down.

To test the effect of novel competitors on plant performance, we transplanted focal alpine species and monoliths containing intact plant communities along an elevation gradient in the Swiss Alps. We simulated different scenarios for the competitive environment that a species could encounter following climate change, in which focal species and/or their surrounding community either do or do not migrate to higher elevations following climate warming. 

Results/Conclusions

Results show that when the focal species failed to migrate, their performance in a warmer climate depended strongly on the identity of the community with which they competed; specifically, their growth and survival was strongly reduced in the presence of competitors from lower elevation, compared to their original alpine competitors. However, community identity did not influence performance when simulating scenarios in which the focal species migrate to track climate change. These results suggest that novel competitors will play an important role in shaping these species’ responses to climate change, and that their ability to persist in the face of climate warming will depend strongly on the rate of immigration of competitors from warmer areas. Therefore, explicitly accounting for novel competitors could underpin our ability to accurately predict species responses to climate change.